The invention is especially suitable for use aboard ship wherein an antenna is operated to track a transmitting station, such as a communications satellite, notwithstanding roll, pitch, yaw, and turn motions of a ship at sea.
Antennas used in shipboard satellite communication terminals typically are highly directive. For such antennas to operate effectively they must be pointed continuously and accurately in the direction toward the satellite.
When a ship changes its geographical position, or when the satellite changes its position in orbit, and when the ship rolls, pitches, yaws and turns, an antenna mounted on the ship will tend to become misdirected. In addition to these disturbances the antenna will be subjected to other environmental stresses such as shocks caused by wave pounding. All of these effects must be compensated for so that the antenna pointing can be accurately directed and maintained in such direction.
Cost, compactness in size and lightness in weight are of paramount importance for antenna pedestals used on ships. Small ships and boats which operate in rough seas routinely experience roll amplitudes of +/−35 degrees or more, pitch amplitudes of +/−15 degrees, and repetitive wave pounding shocks of 5 g's or more. Antenna pedestals which are compact and light yet rugged are highly desired.
U.S. Pat. No. 5,419,521 discloses a three-axes pedestal for a tracking antenna. While this pedestal is quite effective, additional stabilization may be necessary, for example, during extremely rough seas and gale force winds.
U.S. Pat. Appl. No. 2010/0149059 discloses an improved three-axes pedestal for a tracking antenna. This pedestal includes horizontal and vertical vibration isolation components to better isolate the antenna from vibration and shock received by the base of the pedestal. However, the servo systems required to control the angular position of the antenna mounted on this pedestal is rather complex and sensitive to imperfect balance, bearing friction and imposed vibration and shock.
It would therefore be useful to provide an improved pedestal for a tracking antenna having shock and vibration isolation components allowing the position of the tracking antenna to be controlled by relatively simple servo systems and by use of simple stepper motors and a servo mechanism that is much less sensitive to imperfect balance, bearing friction and imposed vibration and shock.